1. Field of the Invention
The present invention relates to the field of corrective orthopedic surgery.
It concerns an implant intended for osteotomy operations. More precisely, the invention is relative to a calcanean translation plate.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The skeletal bones of human beings and vertebrates generally consist of at least two areas: a rigid cortical area and an internal spongy area of more tender consistency which may itself, for certain bones, be traversed by a marrowy canal enclosing soft tissues.
The human hindfoot is essentially comprised of two bones: the ankle-bone (or astragalus) above which is placed on the calcaneum below. The calcaneum is a short bone, even and asymmetric, of elongated shape from the rear end forward and flattened across. The association of the calcaneum and the ankle-bone forms the heel on which rests most of the body's weight. This part of the foot is therefore subject to heavy pressures which makes it prone to various malformations, sources of pain and difficulty and/or incapability of walking for the patients.
It is sometimes indispensable to correct the shape of the calcaneum. The intervention consists of an osteotomy of said bone with medialization of the large tuberosity, i.e. the section of the calcaneum into two parts and the displacement of one in relation to the other. This will allow a better support of the hindfoot and above all reducing the internal constraints on the muscles and ligaments.
Osteotomy designates the surgical section of a long bone in order to modify its axis, size or shape for therapeutic or plastic purposes; it is directed at restituting better axes to long bones in order to better distribute the pressures on the corresponding articulations. Then, the principle is either to cut out a slice over the width of the bone, and to refasten the remaining pieces after having removed it, or to simply cut across and to open the space of one side, by filling the void created with a bone graft, depending on whether one wants to close an angle or open it. Osteotomy may also be followed by a translation, i.e. the shifting of one of the parts of the bone resulting from this section.
This operation requires the installation of support systems for the calcaneum in order to keep the translation in place. As far as the calcaneum is concerned, this part of the foot being subjected to very strong pressures due to the weight of the body and its role in walking, the major difficulty is to produce orthopedic systems that are sufficiently stable and rigid to remain in place and maintain the translation of the calcaneum.
One knows of calcanean implants of diverse and varied shapes, but the perpetuation of the system, i.e. its lasting stability and rigidity, is often uncertain because the implant rests generally in the spongy part of the calcaneum, in spite of the locally harder thalamic crossings, which leads to a rotation of the system as well as a slipping of the latter under the effect of the forces of the body's weight and the porosity of the spongy part of the bone.
For example, the document US-2011/009.866 describes a system for osteotomy composed of a plate which includes two ends aligned along a longitudinal axis fitting together through a median portion and screws. The first end includes a cutting edge and a hole which receives a non-interlocking screw and presents a chamfer which narrows from a lesser thickness at the edge in the direction of the hole, the second end has a locking hole which receives a safety screw, and the first and the second hole are aligned along the longitudinal axis.
The drawback of this device is primarily the lack of stability: as a matter of fact, the configuration of this implant does not allow it to be supported by the cortical of the proximal end of the calcaneum. Its only support therefore is the spongy bone which is porous. In view of the extremely strong forces being applied to this bone, in particular during walks, this system is liable to enter into rotation or slide in the spongy part of the proximal portion of the calcaneum which makes it very unstable and presents major risks for the patient.
Also known are calcanean implants which have no compressive effects on the orthopedic screws allowing their fixing, or for which the locking of said screws is done with a metal-metal coupling which leads, over time, to a cold solder of the galvanic couple leading to toxic corrosion for the patient and making the later removal of the screws impossible.
Furthermore, these implants present the drawback of requiring particularly invasive surgery for their installation, forcing the practitioner to make significant opening incisions over the entire lateral portion of the calcaneum.